Field of the Invention
The invention relates to the production of bio-diesel in general and high efficiency production of bio-diesel in particular.
Prior Art
The production of bio-diesel from waste oils is known. The feed stock is commonly comprised of glycerides and free fatty acids. Glycerides consist of one to three long chain fatty acids bound to a glycerol molecule. Glycerides are often present in the form of vegetable or animal oils or fats, such as those available as used cooking grease (fats, oils, and grease—FOG). The feed stock may also often contain soluble and insoluble impurities such as proteins, sugars, detergents, emulsifiers and degradation products of the FOGs generated during their use or storage.
The raw stock is usually quite viscous. In the prior art, the raw stock is commonly heated to temperatures greater than 180° F. to make the raw stock flowable and filterable. Heating the raw stock creates several problems. It is energy intensive, and thus expensive. It also results in the release of volatile organic compounds (VOCs). These either must be captured, which increases costs or they are released into the atmosphere, resulting in pollution. Heating the raw stock is also responsible for the release of nuisance odors into the atmosphere. While not necessarily a health hazard, the emission of these odors is unpleasant for workers and those who work or live proximate to a location where the raw stock is being processed.
Heating the raw stock also has adverse effects on sulfur content. Sulfur is commonly present in the raw stock at levels above 0.1 percent by volume (1000 parts per million or ppm). However, the sulfur contaminants are typically associated with the water phase of the raw stock. Heating the raw stock can cause the sulfur contaminants to disassociate from the water phase and disperse into the FOG. This can make it difficult and expensive to achieve the 0.0015 percent by volume (15 ppm) sulfur ceiling imposed by U.S. federal regulations on highway diesels and even lower sulfur ceilings in place in other countries, particularly in Europe.
Once the raw stock is fluidized and filtered, mono-alkyl esters (bio-diesel) are formed by reacting the glycerides and free fatty acids with alcohol, typically methanol or ethanol, in the presence of catalysts. A catalyst such as a strong acid (e.g. sulfuric acid) is used to facilitate the reaction of alcohol with the free fatty acids. The acid is then neutralized with a strong base such as sodium hydroxide. The stock/bio-diesel mixture is rinsed to remove the salts formed during acid neutralization. Additional strong base and additional alcohol are then added to react with the remaining glycerides to form bio-diesel and glycerol. The glycerol by-product and catalyst are separated and removed and waste water must be removed and treated as well.